The present invention relates generally to methods and apparatus for providing high pressure fluid communication between relatively rotatable, generally coaxial conduits, and in particular to washpipe assemblies such as those used in rotary drilling swivels.
Rotary drilling swivels generally include a washpipe that sealingly engages a set of circumferential seals contained within a seal housing. Frequently, the washpipe remains stationary while the seals and the seal housing rotate. Swivel seal assemblies have conventionally included a series of reinforced, elastomeric, chevron-type seals interspersed with a series of reinforcing back-up rings. Generally, one seal is exposed to full hydraulic pressure on one side, and atmospheric pressure on the opposite side. These seals tend to function in a redundant manner, wherein the full differential pressure of the mud acts on one seal until that seal fails and the next seal in the assembly acts as the primary seal.
The rotating components of the swivel are often subject to some amount of radial misalignment, or dynamic run-out, due to tolerances and inherent operating conditions. Dynamic run-out between the washpipe and the seal housing has normally been compensated for by means of the seal extrusion gap between the two rotating components since most conventional swivel designs have both the washpipe and the seal housing radially fixed relative to their respective mountings. Some prior art swivel designs have sought to compensate for potential run-out and offset problems by allowing the washpipe and the seal housing to articulate.
Current drilling technology has increased the desired operating pressure of rotary drilling swivel seal assemblies to very high pressures. Many conventional swivel seal designs have yielded less than desirable seal life or displayed other unsatisfactory performance in these high-pressure environments. Thus, there remains a need in the art for methods and apparatus for swivel seal assemblies that can withstand high pressures for extended periods of time. Therefore, the embodiments of the present invention are directed to methods and apparatus for swivel seal assemblies that seek to overcome the limitations of the prior art.